1. Field of the Invention
The present invention relates to an envelope sheet used for manufacturing an envelope.
2. Description of the Related Art
In recent years, along with expanding use of envelopes for direct mails or the like, various types of envelope sheets used when manufacturing envelopes with an automatic envelope manufacturing system have been developed (Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2000-343892). The configuration of an envelope sheet according to prior art is as follows.
The envelope sheet according to prior art has a first rectangular component sheet. A second rectangular component sheet is consecutively connected to the first component sheet along an envelope unfolding direction (sheet long side direction) via a first folding line. A third rectangular component sheet is consecutively connected to the second component sheet along the envelope unfolding direction via a second folding line. In other words, three rectangular component sheets are consecutively connected along the envelope unfolding direction via two folding lines. Here, the first component sheet will serve as the front sheet or the back sheet of the envelope, and the second component sheet will serve as the back sheet or the front sheet of the envelope. The first component sheet has an openable and closable flap on one end side in the envelope unfolding direction.
Coating parts coated with pressure-sensitive adhesive are respectively formed along the envelope unfolding direction, on both side fringes in a direction (sheet short side direction) orthogonal to the envelope unfolding direction in the envelope inner side of each component sheet. In addition, coating parts coated with pressure-sensitive adhesive are respectively formed along the envelope unfolding direction, on both side fringes in the sheet short side direction in the envelope outer side of the third component sheet. Here, a degree of sealing of the envelope can be sufficiently secured by bonding the coating parts of the envelope inner side of the first component sheet to the coating parts of the envelope outer side of the third component sheet, in a state where the coating parts of the envelope inner side of the second component sheet are bonded to the coating parts of the envelope inner side of the third component sheet.
Note that although not clearly described in Patent Document 1, another coating part coated with adhesive for closing the flap is usually formed on the envelope inner side of the flap along the sheet short side direction.
The automatic envelope manufacturing system uses a line head inkjet printing device which can achieve variable printing and high-speed printing. In the line head inkjet printing device, as shown in FIG. 1, the distance (interval) between an endless belt (exemplary conveyance member) which conveys envelope sheets and the inkjet head is about 1 mm, which is very small. Typically, an envelope sheet is printed in a state where the envelope sheet is absorbed toward the endless belt by using, for example, air pressure caused by driving a fan (exemplary absorption member).
The periphery of another coating part of the first component sheet is deformed due to coating of adhesive. If the periphery of another coating part of the first component sheet is largely deformed, absorbing the envelope sheet toward the endless belt cannot correct deformation of the periphery of another coating part of the first component sheet. Thereby, passage of envelope sheets between the inkjet head and the endless belt becomes difficult, as shown by the phantom line in FIG. 1, and a problem may arise such as occurrence of paper jam. Note that, FIG. 1 is a schematic diagram showing a printer in the line head inkjet printing device. In the drawing, reference numerals of respective components of the printer to be described below are provided.